1. Field of the Invention
The present invention relates to a screen pack replacing apparatus, and more particularly to novel improvements for making a filtering area larger than a conventional one and making the overall configuration of the apparatus compact.
2. Related Art
As screen pack replacing apparatuses for a resin extruding machine of this type which have been generally used, a first conventional example is shown in FIGS. 14 to 16 and a second conventional example is shown in FIGS. 17 to 21.
That is, in FIGS. 14 to 16, a main body designated by reference numeral 1 has a resin channel 2 for guiding a molten resin, and the resin channel 2 branches inside the main body 1 into bifurcated first and second channel portions 2A and 2B. In the main body 1, a first slide bar 4, which has a first screen pack 3 disposed in a through hole a formed in correspondence with the channel portion 2A, and a second slide bar 6, which has a second screen pack 5 disposed in a through hole b formed in correspondence with the channel portion 2B, are respectively provided in through grooves 7 and 8, which are provided perpendicularly to the first and second channel portions 2A and 2B, in such a manner as to be slidable by actuators.
Next, a description will be given of the operation. Since foreign objects and the like are captured by the screen packs 3 and 5 during the operation of the extruding machine, the screen packs 3 and 5 must be automatically and periodically replaced during continuous operation. In that case, since either the channel portion 2A or the channel portion 2B must be secured so as not to completely shut off the resin channel 2, if only the first slide bar 4, for instance, is moved by means of the actuator as shown in FIG. 16, the first screen pack 3 is led outside the main body 1, thereby making it possible to replace the first screen pack 3 by means of an unillustrated replacing apparatus.
After the replacement of the first screen pack 3, the first slide bar 4 is returned to its original position, and the second slide bar 6 is then moved to replace the second screen pack 5 in a similar manner.
In addition, in another conventional example shown in FIGS. 17 to 21, four channel portions 2A to 2D, which are formed in an X shape as an inner portion of the resin channel 2 formed in the main body 1, are arranged in a pair of upper and lower stages, i.e., one pair of channel portions for each stage. The first and second slide bars 4 and 6 having the first and second screen packs 3 and 5 and third and fourth screen packs 3a and 5a in through holes a, b, c, and d, respectively, are provided in through holes 7 and 8 provided perpendicularly to the channel portions 2A to 2D in such a manner as to be slidable by actuators 10 and 11.
Next, a description will be given of the operation. First, as shown in FIG. 20, if the first slide bar 4 is moved rightward, the screen packs 3 and 3a are dislocated from the respective channel portions 2A and 2B. As the first slide bar 4 is further moved in the same direction, the first screen pack 3 corresponds to the third channel portion 2B as shown in FIG. 21, and the third screen pack 3a is located outside the main body 1, and can be replaced with a new one.
Also, if the first slide bar 4 is moved in the opposite direction to the one shown in FIG. 21, the third screen pack 3a corresponds to the first channel portion 2A, and the first screen pack 3 is located outside the main body 1, and can be replaced with a new one.
As the second slide bar 6 is similarly moved, the second and fourth screen packs 5 and 5a are replaced.
In addition, in still another conventional example shown in FIGS. 22 to 28, the arrangement provided is such that the slide bar 4, in which the four screen packs 3, 3a, 5, and 5a having substantially the same diameters as that of the resin channel 2 are provided in four through holes a, b, c, and d, is slid in the through groove 7 formed across one resin channel 2 provided in the main body 1, by means of the actuator 10. The respective through holes a to d and the screen packs 3, 3a, 5, and 5a are arranged at predetermined intervals along the longitudinal direction of the slide bar 4.
Next, a description will be given of the operation. First, if the slide bar 4 is moved to the position shown in FIG. 25 by means of the actuator 10, a correspondence between the through hole a and the resin channel 2 becomes approximately one half. In FIG. 26, the pair of through holes a and b and the resin channel 2 correspond to each other by approximately one quarter each, and in FIG. 27 approximately one half of the through hole b corresponds to the resin channel 2. When the slide bar 4 is consecutively moved in this way, and is located at the position shown in FIG. 28, the screen pack 3 in the through hole a is located outside the main body 1. Hence, in this state the screen pack 3 can be replaced with a new one.
As the slide bar 4 is further moved in the same direction in a similar manner, the screen pack 3a can be replaced.
Incidentally, the screen packs 5 and 5a can also be replaced in a similar manner as the slide bar 4 is moved in a direction opposite to the aforementioned direction.
Since the conventional screen pack replacing apparatuses are arranged as described above, there are the following problems.
That is, in the conventional arrangement shown in FIGS. 14 to 16, since a pair of slide bars is required for moving the screen packs, the arrangement is difficult to apply to a large-size extruding machine. Additionally, since a plurality of actuators are required for driving the slide bars, it has been difficult to simplify the structure and reduce the cost.
In addition, in the conventional arrangement shown in FIGS. 17 to 21, there is a position at which the channel of the molten resin is blocked while the slide bar is moving as shown in FIG. 20. In order to allow the molten resin to flow constantly, component parts comprising screen packs, a breaker plate, a slide bar, and an actuator are required in a pair of sets (for upper and lower stages), and it has been impossible to allow the molten resin to flow constantly by means of one slide bar.
In addition, in the conventional arrangement shown in FIGS. 22 to 28, although it is possible to allow the molten resin to flow constantly, in a case where the resin channel 2 and each of the through holes a to d, which are all circular in shape, partially overlap with each other at intermediate positions shown in FIGS. 25, 26, 27, and the like, biased flowing occurs, so that the actual operating filtering area becomes small. Hence, since the filtering area is originally small, the initial pressure loss becomes large, with the result that the frequency of replacement of the screen pack increases, thereby causing a decline in productivity.
Furthermore, as for the slide bar 4, a relatively long one is required, so that the apparatus becomes large in size.